The present invention relates to a fuel cell assembly with at least one fuel cell including an electrolyte layer, a pair of gas diffusion electrode layers placed on either side of the electrolyte layer, and a pair of flow distribution plates placed on either outer side of the gas diffusion electrode layers to define passages for distributing fuel gas and oxidizing gas in cooperation with the opposing surfaces of the gas diffusion electrode layers.
A fuel cell includes an electrolyte layer and a pair of electrodes placed on either side of the electrolyte layer, and generates electricity through an electrochemical reaction between fuel gas such as hydrogen and alcohol and oxidizing gas such as oxygen and air, which are supplied to the corresponding electrodes, with the aid of a catalyst. Depending on the electrolytic material used for the electrolyte layer, the fuel cell may be referred to as the phosphoric acid type, solid polymer type or molten carbonate type.
In particular, the solid polymer electrolyte (SPE) type fuel cell using an ion-exchange resin membrane for the electrolyte layer is considered to be highly promising because of the possibility of compact design, low operating temperature (100xc2x0 C. or lower), and high efficiency as compared to the SOFC.
The SPE typically includes an ion-exchange resin membrane made of perfluorocarbonsulfonic acid, phenolsulfonic acid, polyethylenesulfonic acid, polytrifluorosulfonic acid, and so on. A porous carbon sheet impregnated with a catalyst such as platinum powder is placed on each side of the ion-exchange resin membrane to serve as a gas diffusion electrode layer. This assembly is referred to as a membrane-electrode assembly (MEA). A fuel cell can be formed by defining a fuel gas passage on one side of the MEA and an oxidizing gas passage on the other side of the MEA by using flow distribution plates (separators).
Typically, a large number of such fuel cells are stacked, and the flow distribution plates are shared by the adjacent fuel cells of the same stack. It is necessary to heat the fuel cell stack to a temperature of 80xc2x0 C. to 90xc2x0 C. to promote the electrochemical reaction in each fuel cell. Conventionally, either the entire stack was heated or the peripheral part of each fuel cell was heated.
However, a desired output cannot be obtained within a short period of time from the start up because a certain time period is required for the heat to reach the central part of the SPE. Such a delay may cause an unstable condition of the circuit, which is powered by the fuel cell, or a delay in achieving a fully operative condition of the circuit.
Accordingly, there is need to eliminate such problems in the prior art, and it is therefore a primary object of the present invention to provide a fuel cell assembly that can produce a desired output immediately after the start-up.
According to the present invention, such an object is accomplished by providing a fuel cell assembly with at least one cell including an electrolyte layer 2, a pair of gas diffusion electrode layers 3 and 4 interposing the electrolyte layer 2 between them, and a pair of flow distribution plates 5 for defining passages 10 and 11 for fuel and oxidizer gases that contact the gas diffusion electrode layers 3 and 4, characterized by that: the electrolyte layer 2 includes a grid frame 21 provided with a multitude of through holes 21b, and electrolyte 22 retained in each through hole 21b, heater wire 26 being disposed in a grid bar 21a of the frame 21.
Thus, at start-up, the heater wire 26 disposed in the grid bar 21a of the frame 21 can warm the entire catalyst 3b and 4b and electrolyte 22 to a desired temperature, instead of heating them only locally, so that the desired output can be obtained in a short period of time following the start-up.
In particular, it is preferable that the heater wire 26 is placed on one side or each side of the grid frame 21, and includes of a normal heater wire or film heater wire covered by an insulating layer 27. The heater wire 26 may generate heat either by conduction of electric current or conduction of heat from outside.
Other features and advantages of the present invention will become apparent from the following description with reference to the appended drawings.